Opening at the pace of vaccination

If the case numbers are low, contact restrictions can be relaxed relatively quickly in the course of the vaccination campaign

March 30, 2021

As the number of vaccinated people increases social life can gradually return to normal – but faster so, if infection rates are under control. This is the conclusion of a recent study by a team led by Viola Priesemann, research group leader at the Max Planck Institute for Dynamics and Self-Organization. The researchers calculated the extent to which social contacts can increase with ongoing vaccination without increasing the number of Covid-19 cases. According to the calculations, considerably more social contacts will become possible more quickly if the number of infections is first decreased to a level where the health authorities can once again effectively track and isolate the contacts of virus carriers. The scientists also calculate that even if all people over 80 are vaccinated, intensive care units could still become overwhelmed and thousands of deaths could occur. They also warn that the higher the number of cases during the vaccination campaign, the faster the coronavirus will develop variants that (at least partially) circumvent immune protection.
 

A jab that gives hope: The more people there are that have been vaccinated, the more contact restrictions can be relaxed. However, far-reaching relaxation is possible only once all people over 20 have been offered at least one vaccination.

The Sars-CoV-2 coronavirus is a threat not only to people over 80. Of the 60- to 79-year-old Covid-19 patients, about 5% will require intensive care, and of those in intensive care more than 10% will die. Of the 40- to 59-year-old patients, about 1% will require intensive care, and of those in intensive care almost 7% will die. Vaccinating only those over the age of 80 will therefore not curb the epidemic. With their current calculations, Viola Priesemann and her team show that hospitals will still reach their limits and many people will die if case numbers remain high. The study has been submitted for publication and has not yet undergone the peer review process.

Five scenarios for relaxation during the vaccination campaign

“We are at the crossroads of whether to open at a low incidence of infections or at a high incidence”, says the physicist. “The opening steps are pretty much the same in both cases. However, the number of people with long Covid and the number of deaths is much greater in the case of a high incidence. And more young people will be affected. In order to maintain or achieve low incidences, we have to remain patient for just a little while longer. But then we can open faster than if we opened when case numbers are high”.

In different scenarios, the Max Planck team in Göttingen simulated how the numbers of Covid-19 cases would be affected if restrictions in public life were relaxed as vaccination progressed. They made various assumptions about the spread of the virus and the strength of immune protection. However, these were subject to certain uncertainties. For example, they assumed that vaccinations provide an average of 90% protection against severe disease progression and 75% protection against transmission of the infection and that 80% of people over the age of 20 would get vaccinated. In the first scenario, the measures would be largely relaxed immediately. As a result, intensive care units would fill up within a few weeks. “In order to prevent the capacity from being exceeded, the restrictions will then have to be tightened again”, says Priesemann. “The freedom would thus only be short-lived.”

Cautious relaxation may be possible depending on the progress of vaccination

In three scenarios, the Göttingen researchers calculated the development of case numbers and deaths as well as the occupancy of intensive care units if the restrictions are reduced at different stages of the vaccination campaign. Cautious relaxations are possible on a continuous basis – but must be coordinated with the progress of the vaccination. The three scenarios differ as to when mayor restrictions are lifted, namely as soon as everyone over 80, over 60, or over 20 has been offered vaccination. In all three cases, there are further waves of infection, albeit of varying severity. These will push the intensive care units to their limits – even when all those over 20 have had the opportunity to be vaccinated. “This is because even the best vaccination does not provide 100% protection against a severe course of the disease”, explains Priesemann. It must also be taken into account that not all people want or are able to be vaccinated and that the vaccine is not approved for children and adolescents. “The fact that the immunisation wears off over time and that there may be a spread of new virus variants is not even taken into account here”, says Simon Bauer, who was substantially involved in the calculations.

As increasing numbers of people are vaccinated, the number of social contacts can gradually increase compared with the current situation. More freedom is possible only if the number of new infections is so low that the health authorities can effectively trace and isolate contacts of virus carriers (dashed line). At the points marked with asterisks, the contact restrictions could be relaxed to a large extent – for the scenario that the health authorities can work effectively and for the scenario that the case numbers are too high for this (solid line). From these points onwards, adhering to the DHM+V+A rules and restricting large gatherings will be enough to curb the number of cases. Seasonality effects lower this threshold over the summer so it can be reached earlier.
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However, as long as there is no spread of new and more contagious variants, only minor precautions would need to be maintained in order to prevent a new wave following the vaccination of all those over 20 years of age. Adherence to the so-called "AHA+LA" rules (distance, hygiene, masks, ventilation, and corona warning app), increased testing, and the avoidance of large events should then be enough to keep the incidence low. Waiting with extensive relaxation of restrictions until all people over 20 can be vaccinated will thereby cost about 9600 fewer lives by the end of the vaccination campaign – compared with extensive relaxation of rules after all people over 80 have been vaccinated. “Purely for ethical reasons, it is advisable to lift the measures at the earliest when all people over 20 have had the opportunity to be vaccinated”, says Priesemann.

Compared with immediate and extensive relaxation, a greater epidemiological effect could be achieved if the case numbers were permanently kept low enough for health authorities to make a significant contribution to containing the epidemic. Experience from the second wave shows that for this to happen, the observed incidence would have to be well below 50. “We would then see only about 7000 more deaths – compared with more than 27,000 deaths if the restrictions are lifted immediately after the 80-year-olds have been vaccinated”, says Bauer. “The number of ICU patients and long-Covid cases would be reduced even more significantly”.

With high numbers of cases, the virus learns to circumvent vaccination protection

The scenario with low case numbers also has the lowest risk of the virus mutating and circumventing vaccination protection. That’s because when many people become infected with Sars-CoV-2, it can act like a “training camp” for the virus. The virus variants not immediately recognised by the immune system have a better chance of multiplying and then spreading throughout the population. Such virus variants are therefore referred to as “escape mutations”. The vaccinations are less effective against them. In the worst case scenario, vaccination will have to be started all over again because of an escape mutation. This would be an immense burden on health, society, and the economy. Viola Priesemann therefore emphasizes: “In order to delay the emergence and spread of an escape variant in Germany, it is important to keep the case numbers as low as possible”.

However, it should become easier to reduce the incidence in the coming months. According to the German and the European vaccination plan, the immunity of the population will grow, and the seasonality of the epidemic will also have an effect. “It comes down to using the progress of vaccination as a benchmark for the relaxation of rules. If we open faster than the vaccination progress allows, the intensive care units will be full again within a matter of weeks. If we open a bit more slowly and there are no escape mutations, the case numbers will decrease. We can then look forward to a summer with more freedom than in 2020”.

PH

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